Means for touching up radio photographs



J. E. SMITH MEANS FOR TOUCHING UP RADIO PHOTOGRAPHS 3, Filed Aprjil 20.1939 :Si i i5 minar/VIV mma/rdn! mannaro@ mom/avrai l//V Z/ 4/ 6/ que.'I L I 5 afar/nn inviati AAAAAAA ATTORNEY.

other effects.

Patented Dec. 3, 1940 PATENT OFFICE MEANS FOR TOUCHING Ur RADIO iPHOTOGRAPHS James Ernest smith, Brooklyn, N. Y., assigner to RadioCorporation of America, a corporation of Delaware Application April 20,1939., Serial No. 269,055

` 2 claims. (c1. 17a- 6.7)

This invention relates to photo radio reception.

In facsimile andfother photo radio transmitting systems 'the receivedsignal often fades to, and below, the noise level during adversemultipath effectsin the upper atmosphere. The effects Vappear aspronounced'streaks in the received picture.` These streaks are eitherwhite or black, .depending upon the polarity of modulation. It is anobject of my .invention to touch up the streaks in receivedVpicturesldue to fading and Another object of my invention is to addlocal indications that convert the' white or black streaks in fadingeffects to gray so 'that they are not particularly noticeable.

Other Objectswill appear in the following description, reference beinghad to the drawing in which:

Fig. 1 is a block vdiagram illustrating a photo radio transmitter.

` Fig. 2 isia block and diagrammatic illustration of a receiving4systemj employing my invention.

Fig.' 3'v shows graphs' illustrating principles of my invention. 7 f

Fig. 4 shows the voltage attenuation curve of the demodulator.

While my invention is useful with other forms of modulation I haveillustrated it in connection with facsimile and other photo radiosystems in which themodulations are produced by Varying the frequency ofthe carrier.`

Referring to Fig. 1, scanning device I has its varying output feedinginto modulator 2 varying la sub-carrier frequency produced by lowfrequency generator 3. The varying frequencyfoutput containing thepicture modulations pass into modulator 4 which varies the amplitude ofradio frequency generator 5. Theoutput of modulator 4 passes intotransmitting apparatus 6 and the signal is radiated by antenna 'I. 'Ihescanning apparatus` I, frequency modulator 2, generators 3 and 5,amplitude modulator 4, transmitting apparatus 6 and antenna 'I may be ofany desired form and the details of these are no par-t of my invention.Consequently they are shown and described only generally for a clearerunderstanding of my improvement which resides particularly in thereceiving system. At the receiver end of the system the modulated'signalis received on antenna 8 and is amplied, detected and further amplifiedby the receiving apparatus 9. The output of receiver 9 thereforeconsists of the variable subcarrier frequency which `contains thefrequency modulations imposed at the distant transmitter.

In general this also will contain modulations and fade-outs produced bystatic and other atmospheric causes. This low frequency output fromreceiving apparatus B passes into limiter I0 which cuts off portionsofthe negative and positive halves of .the waves and thus eliminates theamplitude modulations produced by fading.' Complete fade-outs, orfade-outs that descend into the noise level, are not eliminated bylimiter I0 and it is here that my improvement enters. output of limiterIll is fed into a switching device II which preferably is` of theelectron type described in my joint application, Serial No. 270,332, ledApril 27, 1939. The particular type of switch forms no part of myinvention claimed l5 herein randtherefore to simplify `the disclosure iand aid in its understanding I have illustrated the switch I I4diagrammatically only, but it would be understood that the `details ofthis switch will not beof the simple type actually disclosed. As 20Ihave thus illustrated it, the output of the limiter I0 has controllines I3'feeding into control coil I4 and output lines VI 5, thecontinuity of which is controlled byswitching device Itunderv control ofcoil.I4'. The switching device I6 also controls 25 the continuityoflocal generator IIwhich produces thetouching Iup energy that eliminatesthe-white or blackstreaks caused byffading; as previously referred to.The output lines I8 from the switch II are connected to a'frequency de-30 modulator converter I9 which may be of any `sort but for simplicityof disclosure I have shown it as a high pass lter containing seriescapacity and shunt inductance. The output of the converter passes into'appropriate rectifying and re- 35 cording apparatus generally indicatedat 2t. The receiving, detecting and amplifying apparatus 9 and therectifying and recording apparatus 20 may be of any sort as thesedevices are old and well known. The limiting apparatus I0 may 40 also be-of any desired type but preferably it would be that shown in my jointapplication above referred to.

The operation of the 'system will be as follows:

The scanning apparatus will modulate the sub- 45 carrier frequency ofgenerator 3 and 6 and the varying frequency output willamplitude-modulate the radio frequency carrier 5. 'Ihe subcarrier may beof any desired low frequency but a band within the range of 800 cyclesto 2000 50 cycles mentioned in my joint applicati-on above referred towill be found satisfactory.

The output of modulator 4 passes into the transmitting apparatus 6 atthe transmitting statien and is radiated by antenna I. The antenna 55The 1 Cil 8 of the distant receiver in Fig. 2 will receive the modulatedradio frequency carrier and this will be appropriately amplied at radiofrequency, detected and amplified at audio frequency by the receivingapparatus 9. The output of this receiving apparatus is illustrated bygraph A in Fig. 3, where the varyingk frequency of the modulatedsub-carrier is clearly indicated. The fading effects are also indicatedin this graph and between the points a and b it will be noted thatsubstantially a complete fade-out has occurred; When the wave is passedthrough the limiter l the output will be as indicated by graph Bof Fig.3. This of course has the variable frequency present in graph A butthepeaks havev been eliminated by passage through this device, but ythewave is substantially completely blocked out betweenV the lines a and b,asin-'graph A. When ythis portion of the wave reaches the .switch ll thecontrol device typified by Ill,r I6, will switch out the control lines'l5 from limiter vI0 ,and will switch in the local oscillatorl1. Thislocal oscillator will therefore fill in the graph-'at al with energy ofthe sameamplitudre ,and constant frequency 'as'indicated ObviowlylimiterIlor another limiter can be placed after the switch Il amplitude for thelocal energi7 if desired so that'the output will have the same as wellas that coming from the receiver.

If the upper limit of the modulation band F2 (Fig. 4) is 2000 cycles,and the, lower limit F1 is 1000, then the frequency of local oscillatorIl will be adjusted to have a frequency of Fo substantially half waybetween these two values. This means ythat when the fade-out occurs asbetween the lines a, b, in graph A instead of having a white streak or ablack streak, asthe vcase maybe, there will be a gray portion which isneutral and `will be substantially unnoticeable.

As soon as the point B is reached, the voltage,

in coilfd will be such as to lthrow the switch I6 to pass the energy inlines I tothe frequency demodulator I9 and interrupt the source.v

In this way as the ,signal fades out or into the noise level instead`ofthe blackxork white. streak in any particular type of recorder, agrayportion will beproduced that has a less harsh'orfpleasing appearance. Inother words, my 'improvement vautomatically touches up the defects ofthe recorded picture somewhat analogous to the touching up of a pictureby a photographer, but of course it is done at high speed by theelectron type of switch and it is entirely automatic. Instead of usingmy improvement with frequency modulated signals which areV convertedinto varying amplitude signal voltages V1, Vo V2, by the varyingfrequencies, as indicated in"`Fig.4, it will be quite apparent that thesame effect can be produced when variable amplitude modulation isproduced by the scanning apparatus, as the constant output and constantfrequency of local generator Il would still produce a medium amplitudethat would produce gray in the picture.

In disclosing my improvement I have necessarily referred to particularlapparatus but this has been by way of example only and variousmodifications may be used without departing from the spirit of theinvention.

Having vdescribed my invention, what I claim is:

l. In signalling apparatus, a source of frequency modulated signalwaves, a local source of oscillations having constant frequencyintermediate the upper and lower limits .ofthe frequency modulation ofthe signal waves, means .for limiting the amplitude ofthe frequency.modulated waves to eliminate spurious amplitude increase, and means todemodulate the frequency modulation of the signal waves when the signalstrength is above a predeterminedfvalue and to demodulate the constantfrequency modulation of the local source when the signal is therebelow.

2. In signalling apparatus, asource of frequency modulated signal waves,a' demodulator for converting the rfrequencymodulation into amplitudemodulation, a local source of oscillations having a constant frequencyintermediate the upper and lower limits of the frequency modulation ofthe Ysign-alwaves, means for limiting the amplitude of the 'frequencymodulated waves tol eliminate spurious amplitudeincrease,

and means for connecting therdemodulator to the limiter to receive thesignal wave whenit is above a predetermined amplitude and to the localsourcev

